As part of a standard toxicological evaluation, all new products must be tested to insure they are not genotoxic. Animal tests are available but European legislation that takes effect in 2009 will ban animal testing. This legislation will affect almost all large US multinational personal care, cosmetic, and pharmaceutical companies. Non-animal, in vitro tests exist;however, they lack specificity and result in an unacceptably high rate of false positives. This leads to a large number of materials being excluded from further development even though are safe. The long term goal of the proposal is to validate an in vitro test method to accurately determine human skin genotoxicity. Phase 1 research made significant progress in developing a reconstructed skin micronucleus (RSMN) assay for genotoxicity testing. A standardized protocol, a pre- screen cytotoxicity assay, and a prediction model (based on statistically significant increases in micronuclei in dividing cells) were defined and tested. A previously published method was improved to increase the sensitivity of the assay for detecting genotoxins requiring metabolic activation. In addition, long term reproducibility studies utilizing tissue from multiple donors showed highly reproducible results. Phase 2 will further build on Phase 1 results to optimize the assay method, automate scoring, expand the database of materials tested, demonstrate interlaboratory reproducibility, and adapt the assay to a high throughput format. These studies will lay the groundwork for formal validation and regulatory acceptance of the assay. PUBLIC HEALTH RELEVANCE: Current genotoxicity test methods rely on animals or in vitro tests. However, the in vitro methods give an unacceptable percentage of false positive test results and animal testing will be banned for US based multinational companies due to pending legislation. This project will develop an in vitro assay which accurately predicts human genotoxicity.